1. Field of the Invention
The invention relates to an apparatus for slicing fibrous feed material, in particular, trunk wood. The apparatus comprises a slicing device which rotates about an axis and is, for example, in the form of a blade ring, a blade shaft, or a blade disk, wherein the slicing device comprises slicing tools each comprising a blade carrier and a blade unit. The cutting blade edge of the blade units define a common cutting blade edge circle or a common cutting blade edge plane. The feed material is supplied in working cycles in the direction of its longitudinal axis to the blade units. Slicing is carried out in a direction parallel to the fiber orientation by producing a relative movement transverse to the fiber orientation between the feed material and the blade units. On the end face of the slicing tools, respectively, a cutting element acting transverse to the fiber orientation is arranged for producing a separating cut in a separating plane between two slicing cycles.
2. Description of the Related Art
In the utilization of wood as a basic construction material, structural parts which are comprised of glued wood chips or strands are becoming more and more import as a result of their greater and more constant strength across their length as well as their shape stability. These structural parts include, for example, OSB (oriented strand board) products. These structural parts furthermore have the advantage that high-quality products can be produced from recycled wood or trunk wood of lesser quality, wherein an almost complete utilization of the starting material is possible.
For producing the strands or flakes as the starting material for such structural parts, it is known to employ slicing devices comprising blade rings, blade shafts and blade disks comprising slicing blades. These devices have in common that the cutting edges of the slicing blades are arranged on a common cutting edge circle or a cutting edge plane which the cutting edges describe when the device is rotated. By performing a relative movement between the feed material and the slicing device, the cutting blade edges are brought into engagement with the feed material such that the cutting blade edges are parallel to the fiber orientation of the feed material.
It is conventional in connection with feed material having substantially only a longitudinal extension, such as, for example, trunk wood, to perform the slicing operation in cycles. In this connection, the trunks are combined to a bundle with parallel fiber orientation and are fed with their end facing the slicing device in the axial direction into the slicing space while being supported at the opposite end outside of the slicing space. By generating a relative movement between the trunk wood and the slicing tools, the slicing action takes place and the length of the trunk wood is shortened by the depth of the slicing space. The next portion of the wood bundle is then fed into the slicing space, and a new working cycle begins.
The quality and the properties of the final product are greatly affected by the geometry of the flakes or strands used in their manufacture. In order to ensure constant material properties, it is necessary to employ strands of uniform dimensions with boundary surfaces that are as smooth as possible. The slicing geometry is determined by the amount of radial projection of the cutting edge into the slicing space, which determines the strand thickness, as well as the spacing of the cutting edges relative to the strand breaking strip which is recessed relative to the cutting edge and which determines the width of the strand.
The determination of the length of the strand is realized by providing so-called scoring members which carry out a leading cut transverse to the fiber orientation with their radially acting cutting edges before the strand is lifted off by the subsequent slicing blade. The scoring members are arranged in the immediate area of the blade carriers and the slicing blades and are positioned circumferentially in radial planes which are staggered in the direction of the depth of the slicing space, wherein the axial spacing of two radial planes determines the length of the strand.
Problems when using such scoring members are caused by the more-than-average great loading during operation of the slicing apparatus in combination with the requirement to embody the scoring members as narrow as possible in order to maintain the flank pressure in the area of the cutting edge of the scoring member as small as possible. In order to provide a satisfactory solution in this connection, it is known to design the scoring members as thin as possible and to arrange them in precisely fitting slots within the blade carrier so that only the cutting edges project past the slot. The positive-locking securing action on both sides results in a rigid clamping action of the scoring member which protects the scoring member from being overloaded in a direction transverse to its plane. This arrangement of the scoring member however is possible only over the length of the slicing blade or the blade carrier, but is not possible on the end faces of a slicing blade because, as a result of the construction, support on both sides of the scoring member is not possible.
Experiments have shown that the known scoring members, when arranged at the end face of a slicing blade, cannot withstand the load acting thereon so that they will bend or even break off. The broken-off scoring members can enter in certain situations the slicing space and carry therefore the considerable risk of damaging the slicing apparatus.
For this reason, known slicing devices, in general, are not provided with scoring members at the end faces of the slicing blade. Instead, one relies upon the fibers at the end faces of the strand to be torn off during slicing in the separating plane between two working cycles. However, this results in frayed end faces and different lengths of the strands thus produced with disadvantageous effects on maintaining a predetermined strand geometry and thus strand quality. Further disadvantageous after effects are the unsteady running of the apparatus and increased energy consumption.
For the purpose of eliminating these disadvantages, slicing blades whose end faces are provided with an auxiliary blade have already been used. The purpose and object of such an auxiliary blade is to cut off the final strand of a slicing cycle. Even though with this measure the afore described problems could be decreased, the problems could not be solved entirely.
It is an object of the present invention to generate a clean separating cut in the separating plane between two working cycles.
In accordance with the present invention, this is achieved in that the slicing tools have a spacial receptacle or recess for the cutting element, wherein the receptacle or recess is arranged parallel to the plane of the end face of the slicing tools.
Preferably, the cutting element has a thickness of at least 4 mm, preferably 5 mm, with a flank slant angle relative to the longitudinal axis of 20xc2x0-30xc2x0.
Moreover, the blade unit is characterized in that at the end face of the blade unit a recess is arranged for the cutting element which acts perpendicularly to the slicing blade of the blade unit.
By providing a cutting element according to the invention on the end face of the blade unit, the invention overcomes the prejudice of the prior art configurations that scoring members can be arranged only across the length of the slicing blade but not permanently on its end face. Positioning of the scoring members on the end faces in accordance with the invention has the advantage that the strands to be manufactured can also be cut in the separating plane between two working cycles. This results in an improvement of the strand quality because all the boundary surfaces have a smooth surface so that strands with a uniform geometry can be produced.
The slicing action which is realized completely by means of cutting ensures moreover a more quiet running of the apparatus with reduced wear of the slicing tools. Since the work when slicing the strands is not as great as when chipping, there is furthermore the advantage that the inventive slicing apparatus has a reduced energy consumption.
According to the invention, the slicing tools have at their end face a receptacle or recess, respectively, in which the cutting element is arranged, respectively. The receptacles or recesses are formed of at least two surfaces which are matched to the outer shape of cutting element. Accordingly, at least two abutment surfaces for the cutting element are provided which are able to receive the great forces which result during operation of the apparatus according to the invention. This contributes to a significant improvement of the attachment of the cutting elements on the slicing tools.
Instead of a receptacle in the form of a recessed step, it is also possible to provide a shoulder formed at the end face of the blade unit or the blade carrier and projecting therefrom for forming a receptacle. However, a combination of a recessed step with a shoulder is also possible. The unitary shoulder, which according to a further advantageous embodiment can extend up to the outwardly facing side of the cutting element, forms an additional abutment surface and, moreover, an additional protection against mechanical stress of the cutting element as well as against soiling in the area of the cutting element.
According to an advantageous embodiment of the invention, the receptacle encloses the upper side, the lower side, the back side and one of the two lateral sides of the cutting element. This results in an almost complete enclosure of the cutting element and ensures an especially good attachment of the cutting element on the slicing tools and, at the same time, an optimal protection against the penetration of dirt.
A further advantageous embodiment of the invention provides that the receptacle with regard to its depth is smaller than the thickness of the cutting element. This has the result that the cutting element with its outer lateral side projects past the end face of the slicing tool. In this way, the friction surface of the rotating slicing tools relative to the feed material is reduced to a minimum in the plane of the separating cut.
Depending on the configuration of the blade units, the receptacle can be formed partially or entirely by the blade unit. According to a preferred embodiment, the receptacle is formed by the blade unit and the blade carrier. In this connection, the cutting element is arranged with the upper and lower sides between the slicing blade and the wear protection of the blade carrier, wherein the blade holding plate fixedly attached to the slicing blade generates the spacing between the slicing blade and the blade carrier which matches the height of the cutting element.
In this context, it is particularly advantageous when the thickness of the blade holder plate is slightly thinner than the height of the cutting element. When mounting the cutting element, a clamping action is realized which ensures an especially fast and safe securing of the cutting element on the slicing tools.
According to an advantageous embodiment, the cutting element according to the invention has a reduced cutting edge projection length in comparison to the remaining scoring members. By this measure, the inherent high loading of the cutting elements resulting from their configuration is at least partially compensated.
A preferred cutting element according to the invention has a minimum thickness of 4 mm with a maximum flank slant angle of 30xc2x0. This geometry ensures a sufficient own stability in connection with a still acceptable flank pressure.
Such a geometry of the cutting element is of particular importance in connection with a reduced cutting edge projection because the combination of these two features counteracts the flank pressure which increases with increasing thickness of the cutting element.
In a further embodiment according to the invention, the cutting element has its cutting edge arranged external to its center plane wherein the flank slant angle to both sides of the cutting edge has the same absolute value. In this way, the friction between the rotating slicing tools and the stationary feed material can be lowered further in that the separating plane between two slicing cycles can be moved farther into the outer area of the slicing tools.